1. Technical Field
The invention relates to air actuators and more particularly to the clamping means adapted to affix a resilient elastomeric sleeve member to the relatively rigid end caps on each end of the air actuator. Specifically, the invention relates to a clamp assembly for an air actuator and/or air spring employing annular recesses or indentations in the end caps to form a series of pinch areas with the intervening sleeve which sealingly clamp the sleeve therebetween when clamping rings with smooth inner contact surfaces are crimped thereover.
2. Background Information
Pneumatic assemblies such as air actuators and springs, have been used for many years for various purposes. The air actuator usually consists of a flexible rubber sleeve or bellows containing a supply of compressed fluid and a feed for increasing or decreasing the compressed fluid therein. The flexible sleeve is formed of a flexible elastomeric material often containing reinforcing cords, where the flexibility of the material permits a first end cap to move axially with respect to another end cap secured within the ends of the sleeve as the amount of compressed fluid is changed. Since the air actuator is positioned in between a movable or actuatable object and typically a fixed object, the movable object moves in correlation to this axial movement.
As to pneumatic springs commonly referred to as air springs, the construction is similar with a flexible rubber sleeve or bellows containing a supply of compressible fluid. However, the air spring has one or more pistons movable with respect to the flexible sleeve. The piston causes compression and expansion of the fluid within the sleeve as the sleeve stretches or retracts, respectively, thereby absorbing shock loads and/or dampening vibrations. The flexible sleeve is formed of a flexible elastomeric material containing reinforcing cords and this permits the piston to move axially with respect to another piston or end cap secured within open ends of the sleeve. One application for air springs is with motor vehicles where the spring provides cushioning between moveable parts of the vehicle, primarily to absorb shock loads impressed on the vehicle axles by the wheels striking an object in the road or falling into a depression.
In either air actuators or air springs, the ends of the sleeves are sealingly connected to the opposed end caps, or the piston and opposite end cap, respectively, and are always one of the important and major aspects in producing an efficient and maintenance-free air actuator or spring. One problem with certain air actuators or springs is the ineffective sealing and/or clamping of the flexible sleeve to the end caps resulting in a lack of an air-tight seal.
Another problem with existing air actuators and springs is that the exposed cut edge at the end of the elastomeric sleeve of the air actuator or spring will engage the sleeve body as it rolls along the piston or end cap in excessive stroke conditions causing excess wear to the flexible sleeve.
Another problem with existing air actuators and springs is the inability to clamp and grip the flexible sleeve so as to accept high pressures within the fluid pressure chamber within the end-capped flexible sleeve.
Another problem with existing air actuators and springs is the inability to force or flow sufficient rubber from the sleeve into the grooves on either or both the clamp ring and end cap as is needed for sufficient clamping to occur.
Another problem with existing air actuators and springs is that failure of a component end seal at the sandwiching of the sleeve between the clamp ring and the end cap, or failure of an end cap or piston is typically the result when over-pressure occurs and is less desirable versus a sidewall burst of the sleeve.
Another problem with existing air actuators and springs is ineffective holding by the pinch areas, that is the rubber forced into the grooves on either or both the clamp ring and end cap, as is needed for effective high pressure sealing.
Another problem with existing air actuators and springs, and in particular, the clamp ring therefore, is that the clamp ring will move in its clamped position under dynamic conditions causing movement of the clamped elastomeric material therebetween tending to loosen the sealing engagement and deteriorating the clamp integrity and causing ultimate leakage and failure. This ring movement is especially critical during the jounce or collapsing stroke.
Another problem with existing air actuators and springs and the clamping of the elastomeric sleeve ends to the piston member and/or end cap is to secure a sufficiently tight seal to be able to withstand high fluid pressures contained in the fluid chamber without premature leakage or bursting even upon experiencing severe air spring movement and being exposed to the harsh environments on the undercarriage of a vehicle.
Another problem with existing air actuators and springs and the clamping of the elastomeric sleeve ends to the piston member and/or end caps is the time consuming, labor intensive, and expensive process of creating grooves/indentations and/or projections in both the outer diameter of the end caps and/or pistons, and the clamping rings to assure the flexible rubber sleeve does not slide out from between the end caps and/or piston and the ring.
Some examples of air actuators and springs and the end sealing devices thereon are shown in the following patents described below:
U.S. Pat. No. 3,788,628 discloses a pneumatic spring-type system including a structure for anchoring the inner ends of a flexible rolling sleeve. The sleeve is positioned between surfaces characterized by having a saw-toothed shape with a circumferential groove and rib on an inner circumferential surface and two ribs on an outer circumferential surface. The opposite sides of the grooves converge at predefined angles with predetermined and matching radii of curvatures, the combination of which provides a gripping action to hold the flexible sleeve firmly in place by means of the saw-tooth design in cooperation with the matching recess of the ring and sleeve flange.
U.S. Pat. No. 3,870,286 relates to a fluid spring wherein the ends of the rolling sleeve are secured by annular clamping rings which engage against the internal surface of the sleeve. The clamping ring secures the rolling sleeve to the working cylinder with the clamping ring containing an annular groove type deformation by which the rolling sleeve is held in place by virtue of this interacting groove-shaped design in combination with the clamping force exerted by the ring.
U.S. Pat. No. 4,489,474 relates to means for connecting a tubular flexible member to a piston which includes a recess near the piston end which is secured to a flexible member. The flexible member is wrapped over and around a ring-shaped fitting which secures the flexible member to the piston. The piston comprises a circumferentially extending recess adjacent to its end with the flexible sleeve being positioned and substantially filling the recess of the piston. The ring-shaped fitting is a conventional swaged ring and the end portion of the flexible member is trimmed from the portion extending from the piston ring with the flexible member substantially filling the recess of the shoulder of the piston. The piston employs a serrated edge to assist in griping of the flexible member.
U.S. Pat. No. 4,457,692 discloses an assembly for sealing two members, one of which has a cylindrical surface which supports the seal, wherein a sealing lip is provided to bear against the second member. A cylindrical surface supports the seal which comprises a hollow-cylindrical body having a lip which extends outwardly from the body with an elastomeric band circling the body to hold it firmly in place. The cylindrical surface contains a recess which extends circumferentially around the surface and receives a matching projecting element of the seal which extends from the inside diameter of the cylindrical body.
U.S. Pat. No. 4,573,692 discloses an assembly for sealing two members, one of which has a cylindrical surface which supports the seal, wherein a sealing lip is provided to bear against the second member. A cylindrical surface supports the seal which comprises a hollow-cylindrical body having a lip which extends outwardly from the body with an elastomeric band circling the body to hold it firmly in place. The cylindrical surface contains a recess which extends circumferentially around the surface and receives a matching projecting element of the seal which extends from the inside diameter of the cylindrical body.
U.S. Pat. No. 4,629,170 relates to a pneumatic spring with a pair of chambers formed by a pair of membranes that are sealingly attached to an axially spaced-apart retainer and piston wherein the axial end of the membrane is compressed between a serrated surface of a solid member and a retaining ring wherein the ring may be swaged, fitted or otherwise tightened to produce radial compression against the axial ends of the flexible membranes.
British Patent No. 199,789 discloses a metal securing band which grips a diaphragm and forces it against a tapered end portion of a tubular member.
U.S. Pat. No. 4,718,650 shows an air spring in which the ends of the flexible sleeves are connected to the sealing surfaces of a pair of axially spaced pistons by swaged crimped clamping rings. The piston clamping surfaces are formed with serrations for assisting to retain the elastomeric material when forced therein by the clamping rings.
Some of the problems discussed above are solved by the clamping arrangement shown in U.S. Pat. Nos. 4,899,995 and 4,852,861. These patents show the use of a clamp ring having a single centrally located recess which aligns with an outwardly extending projection formed on the sealing surface of the piston and end member in order to position the clamping ring on the piston or end member. A pair of pinch areas are formed on opposite sides of the projection by outwardly extending annular rings or surfaces on the sealing surfaces of the piston and/or end member. These rings form the pinch areas or zones in cooperation with the axially extending inner annular surface of the clamp ring on opposite sides of the concave recess. Although this clamp ring assembly does solve some of the problems discussed above and is extremely efficient for many applications, especially for larger air springs having high internal pressure, it may not provide all of the desirable characteristics demanded by the industry including necessary clamping power, air-tight sealing, and economical production. A disadvantage of the clamping arrangement shown in these two patents is that the clamp rings require a more complicated configuration and, in particular, a recess formed in the center of the inside surface of the ring. This requires a more expensive ring to be utilized in the air spring. It is much cheaper to use a clamp ring in which the inner cylindrical surface is a continuously smooth surface free of recesses, yet achieving the desired clamping force.